mckinnis



Oct. 29, 1963 A. c. McKlNNls 3,109,039

RECOVERY 0F NAPHTHALENIC HYDROCARBONS Filed Jan l5 1961 BJJ CA/J ATTR/VEY United States Patent O 3,lh9,ll39 RECVERY F NAPHTHALENES HYDRCARBNS Art C. Melinnis, Long Beach, Calif., assigner to Union @il Company of California, Los Angeles, Calif., a corporation of California Filed Jan. 13, wel, Ser. No. 82,4% 9 Claims. (Cl. 2613-674) This invention relates to the recovery of naphthalenic hydrocarbons from mixtures comprising the same, and in particular concerns a method of treating hydrocarbon mixtures boiling within the 390 52G F. range and containing naphthalene and/ or alkyl-substituted naphthalenes for the purpose of recovering said naphthalenic hydrocarbons in concentrated form.

The expanding use of naphthalene and alkyl-naphthalenes for the production of dicarboxylic acids useful in manufacturing synthetic resins and iibers has created considerable interest in the recovery of these naphthalenic hydrocarbons from hydrocarbon fractions of petroleum origin. lt is well known that certain fractions obtained from certain petroleum refining operations, eg., catalytic cracking and reforming, contain considerable quantities of naphthalene and alkyl-naphthalenes. However, such fractions also contain large quantities of other hydrocarbon types which have boiling points very close to those of the aforesaid naphthalenic hydrocarbons or which form azeotropes therewith. In either case, satisfactory separation of the naphthalenic from the non-naphthalenic hydrocarbons cannot be accomplished by fractional distillation. Other conventional separation techniques, eg., fractional crystallization, solvent extraction, selective complexing, etc., are equally unsatisfactory for use on a commercial scale.

Accordingly, the principal object of the present invention is the provision of an improved method for treating hydrocarbon mixtures boiling within the 39G520 F. range and comprising naphthalene and/ or alkyl-naphthalenes to separate said naphthalenic materials from nonnaphthalenic hydrocarbons present in the mixture. Other and related objects will become apparent to those skilled in the art as the description of the invention proceeds.

l have now found that the above objects and attendant advantages may be realized in an azeotropic distillation process in which N--nethyl-formamide (HCONHCHB) is employed as the azeotrope-former. More particularly, I have found that N-rnethylformamide forms azeotropics of unusually low boiling point with non-naphthalenic hydrocarbons boiling within the 390520 F. range, so that by admixing N-methyl-formamide with a mixture comprising naphthalenic and non-naphthalenic hydrocarbons boiling within said range, and subiecting the resulting mixture to distillation, an exceptionally efficient separation of the two types of hydrocarbons can be achieved. The non-naphthalenic hydrocarbons distill overhead in the form of low-boiling azeotropes with the N-methylformamide, leaving the naphthalenic materials behind as distillation bottoms. The azeotropic distillate is rich in hydrocarbons and has a relatively low heat of vaporization, so that the amount of heat required to separate a unit volume of non-naphthalenic hydrocarbons from the feed mixture is relatively low. Also, N-methyl-formamide is but slightly miscible with aromatic hydrocarbons, so that in many instances substantially complete separation of the azeotrope-former from the distillate can be achieved by simple gravity settling. ln addition, N- methyl-formamide is essentially non-corrosive and has good thermal stability, and the azeotropic distillation process of the invention is hence not complicated by corrosion or decomposition dimculties.

The process of the invention thus consists in distilling a ice hydrocarbon feed mixture comprising naphthalenic and non-naphthalenic hydrocarbons boiling within the 390- 520" F. range in the presence of sufficient N-methylformamide to vaporize a substantial proportion of the nonnaphthalenic hydrocarbons together with the N-methylformarnide as a minimum-boiling azeotropic distillate, thereby producing an azeotropic bottoms product in which the ratio of naphthalenic to non-naphthalenic hydrocarbons is substantially higher than the ratio thereof in the feed mixture.

Considering now the invention in greater detail, the feedstock to which the distillation step is applied may be any mixture of hydrocarbons comprising naphthalene and/ or alkyl-naphthalenes and at least one non-naphthalenic hydrocarbon which cannot be separated from the naphthalenic component by simple fractional distillation. The term naphthalenic hydrocarbon is herein employed to designate a hydrocarbon compound whose molecule contains the characteristic naphthalene grouping:

Conversely, the term non-naphthalenic hydrocarbon designates a hydrocarbon compound Whose molecule does not contain said grouping. Thus, the non-naphthalenic hydrocarbons which may be present in the feedstock include aliphatic compounds such as dodecane, tetradecane, pentadecane, dodecene, tetradecadiene, etc., naphthenic compounds such as cyclohexylheptene, hexylcyclohexane, dicyclohexyl, etc., benzenoid compounds such as triethylbenzene, dimethyl-propylbenzene, diphenyl, phenyl-Xylene, octylbenzene, dimethyl-indane, ethyl-indene, etc., and partially hydrogenated naphthalenic hydrocarbons such as methyl-tetralin, dimethyl-tetralin, dehydronaphthalene, methyl-dihydronaphthalene, methyl-decalin, etc. The naphthalenic hydrocarbons which may be present in the feedstock include, naphthalene, the methyl-naphthalenes, the dimethyl-naphthalenes, the ethyl-naphthalenes, the isopropyl-naphthalenes, etc.

The feedstock may be derived from any source, e.g., from products obtained by the destructive distillation or hydrogenation of coal, from products obtained in the processing of shale oil, or from various products obtained in petroleum refining. Usually, however, the feedstock will be of petroleum origin. Suitable petroleum hydrocarbon fractions include catalytically and thermally cracked cycle oils, heavy reformate fractions, heavy coker distillate fractions, dealkylated light catalytic cycle oils, etc. The process is particularly well adapted to the treatment of a material obtained by dealkylating heavy reformate fractions. While the feedstock may be one boiling over the entire 39G520 F. range, it will usually be one boiling over only a selected portion of such range (e.g., a fraction boiling at 450-470 F. and comprising monomethyl-naphthalenes, or a fraction boiling 410-435 F. and comprising naphthalene) and may of course contain some components boiling somewhat below or (less desirably) above said range. The feedstock may also be one which has been pretreated to remove part of the naphthalenic components, eg., it may be a dealkylated petroleum hydrocarbon reformate fraction from which at least part of the naphthalene has previously been separated by crystallation.

Procedure-Wise, the process is carried out as a conventional azeotropic distillation operation, and any of the techniques commonly applied to such type of operation are applicable to the present process. In its simplest embodiment, Le., batch distillation, the process consists essentially in adding to the feedstock sufficient N-methylformamide to form azeotropes with the non-naphthalenic system.

components, and thereafter distiiling the mixture in a reasonably efficient distillation column. The azeotropic distillate is condensed and passed to a separator where the condensate is allowed to separate by gravity into two phases, one of which comprises the non-naphthalenic components oi the feedstock containing a small quantity ol N-'nethyl-ormamide, and the other of which comprises N-methyl-ormamide containing a small quantity or" dissolved non-naphthalenic hydrocarbons. Either or both of said phases may be re-distilled or otherwise treated to recover the azeotrope former for reuse. The naphthalenic components of the toodstock are contained in the bottoms fraction which constitutes the desired endproduct of the process.

Two further embodiments of the invention are illustrated in the drawing which forms a part of this application and in which FXGURE l diagrammatically illustrates a simple type of continuous operation, and FIGURE 2 diagrammatically illustrates a somewhat more complex ln the interests o simplicity, the various valves, pumps, heaters, reboilers, reilux condensers, etc. which are characteristic of any distillation system have been omitted from the drawing.

Referring now to FGURE l, a hydrocarbon feedstock boiling over the 46S-510 F. range and containing about 35 Weight percent of allryland dialkyl-naphthalenes and about 65 weight percent non-naphthalenic hydrocarbons which are predominantly aliphatic and naphthenic is introduced into primary distillation column l@ (which may take the form of a 20-8() plate column operated at reiiux ratios of 1:1 to 20:1) wherein it is distilled in the presence of N-methyl-formamide introduced into column lil as a recycle stream through line 2. The azeonopic distillate taken as overhead from the top of column "stl contains about 60 weight percent of N-methyl-formamide and about 4() weight percent of nonnaphthalenic ny rocarbons, and the bottoms fraction remaining in the column contains about 90 weight percent of alkyl-naphthalenes and about l weight percent of non-naphthalenic hydrocarbons. The bottoms fraction Iis withdrawn from column l@ through line 14 as the process product, and may be marketed as such or subjected to further purilication, eg., crystallization. The azeotropic distillate is passed from the top orP column 19 through line to con anser-settler 13 wherein it is condensed and allowed to separate into two liquid phases. The lower phase contains about 97 weight percent of N-methyl-formamide and about 3 weight percent of nonnaphthalenic hydrocarbons, and is returned to column llt? via line 12 as part of the azeotrope-ormer recycle stream. The upper liquid phase in condenser-settler i8 contains about 95 weight percent of non-naphthalenic hydrocarbons and about 5 weight percent of N-methylformarnide. In order to recover the latter, the upper phase is passed via line E@ to secondary distillation column 22 wherein it is subjected to simple fractional distillation. The distillate taken overhead from column 22 consists of the 60-40 azeotrope, and will distill oi only so long as sufficient N-methyl-formamide is present to form said azeotrope. Since the stream fed to column 22 contains only 5 percent of the azeotrope-former, the distillate will be relatively small in volume, and the bottoms iraction which is withdrawn from column 22 via line 2d will consist of substantially pure non-naphthalenic hydrocarbons. The distillate from column 22 is passed via line 2d to a second condenser-settler 23 wherein it condenses and separates into two liquid phases. The upper phase in condenser-settler ZS has the same composition as that in condenser-settler 13, and is combined therewith and is returned to column 22 via line 2). Similarly, the lower phase in condenser-settler 2S has the same composition as that in condenser-settler l, and is combined therewith and returned to column it) via line l2. As will be apparent, this simple system continuously produces ,inane-s ln the preceding description made with reference to the processing system of FGURE 1, it will be noted that the non-naphthalenic components of the feedstock 'ere predominantly aliphatic and naphthenic hydrocarbons, and that a relatively good separation of azeotropeformer from hydrocarbons is obtained in condensersettlers ill and 28. However, when the non-naphthalenicv components of the feedstock comprise a higher proportion of benzenoid compounds, particularly lower alkylbenzenes, such separation will not be so complete, and it may be desirable to make use of a so-called miscibility reducing agent to decreasethe solubility of N-methylformamide in such hydrocarbons, or to reduce the solubility of the latter in N-rnethyl-formamde. Usually, it is preferred to employ such an agent when the solubility ot N-methyl-forrnamide in the non-naphthalenic hydrocarbons, or vice versa, is greater than about 20 percent. Any non-reactive material capable of reducing the miscibility of N-methyl-formamide and hydrocarbons may be employed as such an agent, and in general such materials will be miscible with N-rnethyl-formamide and immiscible with hydrocarbons, eg., water, or miscible with hydrocarbons and immiseible with N-methyl-formamide, eg., an aliphatic or naphthenic hydrocarbon such as decane or cyclohexane. FIGURE 2 illustrates a processing system in which a miscibility-reducing agent is employed and in which auxiliary equipment is provided for further processing of the recovered naphthalenic hydrocarbone.

Referring now to FiGURE 2, a wide boiling range feed-stock containing naphthalene, methyl-naphthalenes and dimethyl-naphthalenes as naphthalenic components and various other hydrocarbons, including a high proportion of allcylbenzenes as non-naphthalenic components is introduced into primary distillation column 30 wherein it is azeotropically distilled in the presence of N-methylformamide introduced into column Sil as a recycle stream from line 32. The distillate, comprising the azeotrope of N-methyl-formamide and the non-naphthalenic components or the feedstock, is taken otf the top of column 39 and is passed via line E54 to condenser-settler 36. Prior to the start of operations, suicient Water (eg, 10 percent by weight of the N-methyl-formamide employed) is charged to condenser-settler 36 to reduce the solubility oi N-methyl-formamide in the non-naphthalenic hydrocarbon components of the feedstock to a low value, eg., below about l0 percent. Consequently, the upper layer which forms in condenser-settler 36 contains less than l() percent of N-methyl-formamide, in contrast to the 15-20 percent which obtains in the absence of the added water. Said upper layer is withdrawn from the condenser-settler and is passed to secondary distillation column 38 via line Column 35 produces a small overhead stream consisting of the azeotrope, which is returned to condenser-settler 36 via line 42, and a bottoms fraction consist-ing of non-naphthalenic components of the feedstock which is passed to storage via line 44. The lower liquid layer which forms 'in condenser-settler 36 consists essentially of wet N-methyl-formamide. It is passed via line 46 to a small distillation column 4S. The overhead from column 43, consisting essentially of water, is returned to condenser-settler 36 via'line 42, and the bottoms fraction, consisting essentially of N-methyliormamide, is returned to column 3l) via line 32 as the aforesaid recycle stream. The bottoms fraction produced in column 39 consists essentially of the naphthalenic components of the feedstock. It is passed through line 59 to a crystallization operation whereby the naphthalene is sena-rated in solid form. The mother liquor,

consisting of methyland dimethyl-naphthalenes, is passed via line 52 to a third fractional distillation column 54 to produce a methyl-naphthalene overhead fraction boiling at about 455-470 F. and a dimethyl-naphthalene bottoms fraction boiling at about 480-510 F.

Fraction No. 7, an additional 100 volumes of N-methylformamide is added to the still pot. The phases are separated, and the upper phases of certain of the fractions are analyzed for hydrocarbon types. The analyses and details of the distillation are summarized as ffollows:

Analysis, percent by Wt.

Upper Lower Vapor Fraction No. Layer Layer Temp., Aliphatics Naphtlialenics Volume Volume F. and Benze- N aphnoids thenies Cw Cn C12 C13-l- Example ll The following example illustrate the practice of the invention in its simplest embodiment, and provide 1a quantitative demonstration of the eilciency with which the subject separation is achieved, but are not to be construed as limiting the invention:

Example I A catalytically cracked cycle oil (boiling range=408 520 F.; density=0.85) having the follow-ing analysis as to hydrocarbon types:

Percent by weight 65 N on-naphthalenics Aliphat-ics 22 Naphthenics 23 Benzenoids Naphthalenics Methylnaphthalenes 9.8 Dimethylnaphthalenes 22.2 Others 3.0

is `fractionally distilled in la l0-plate Oldershaw column at a 10:1 reflux ratio and in the labsence of Ndmethylvformamide. The distillate is collected in thirteen fractions of approximately equal volume, and each of said fractions, together with a small bottom fraction, is analyzed for naphthalenic compounds. The analysis is as follows:

Volume, percent oi Feed Naphthalentes, percent by Wt.

Fraction No. Vapor Bottoms The processing system employed corresponds to that shown in FIGURE 1, with column 10 taking the `form a 50-plate bubble-cap tower and operating at a reflux ratio of 8:1. The feed stream is a blend of bottom fractions obtained in the catalytic cracking and platinum-catalyzed reforming of a naphthenic petroleum fraction, said blend boiling over the range of about 400-550 F. (true boiling points) and analyzing as follows:

Percent by Weight The feedstock is continuously introduced into column 110 along with an approximately equal volume o-f recycled wet N-methylformarmide containing about 8 percent by weight of Water. The column is operated to produce an overhead stream Iat a vapor temperature of about 380 F. and a bottoms fraction boiling labove about 420 F. The latter fraction is continuously withdrawn from the bottom of column 10 as the process product, `and comprises about percent by weight of naphthalene Iand methylnaphthalenes. The overhead from column 10 is passed to condenser-settler 18 wherein it separates into an. upper hydrocarbon layer, comprising about 96 percent by Weight of non-naphthalenic components l `of the feedstock and of about 4 percent by Weight o-f N-methylaformamide, and a lower Wet N-methylform amide layer. The latter .is returned to colum 10 as part of the N-rnethyl-formamide supply thereto. The upper hydrocarbon layer is Withdrawn from condenser-settler 1S and is passed to column 22 which takes the form of a 20-plate :bubble-cap tower operated at a reilux lratio of about 5:1. The overhead fraction from column 22 is Withdrawn at la vapor temperature of labout 380 F., and is passed to condenser-settler 28. The 'bottoms fraction from column 22 is withdrawn therefrom and is passed to storage as the non-naphthalenic process product `containing less than 5 percent by weight of naphthalenic hydrocarbons. The upper layer in condenser-settler 213 is recycled as part of the feed to column 22, and the lower layer, consisting of Wet N-methyl-formamide and being essentially aio-aces free of hydrocarbons, is returned to column lit as part of the N-rn'ethyldorniamide supply thereto.

Example III A bottoms fraction of e. platinum-catalyzed reformer product (boiling range=385440 F.) is hydrodealkylated over a cobalt oxide-molybdenum oxide catalyst to produce a dealkylated product boiling over the range 141- 550 F. This product is fractionally `distilled to obtain a light gasoline fraction `boiling at l4l40l F., a naphthalene fraction boiling at 401-438 F., a methyl-mph thalene fraction boiling at 456-467 F., and a heavy fraction boiling at 493-550 F. Analysis shows lthe methyl-naphthalene lfraction to contm'n about 90.5 percent by weight of land Z-methyl-naphdxalenes and about 9.5 percent by weight of non-naphthalenic hydrocarbons, presumably alkyltetralins `and alkylindanes. This material, together with 20 percent by weight` of N-rnethyl-formamide, is introduced into column 1t) of the processing sys tem' shown in FTGURE 1, and the distillation is carried out as previously described. The naphthalenic product withdrawn yfrom the Ibottom of column 1t) contains about 98.5 percent by weight of methyl-napht-halenes.

Other modes of applying the principle of my invention may be employed instead of those explained, change being made as regards the materials or methods employed, provided the step :or steps stated by any of the following claims or' the equivalent of such stated step or steps, be employed.

L therefore, particularly point out and distinctly claim as my invention:

l. A process for treating a hydrocarbon mixture boiling within the range from about 390 P. to about 526 F., and comprising naphthalenic and non-naphthalenic components which are not separable by simple fractional distillation, which process comprises azeotropioally distilling lsaid mixture together with added N-methyl-formamide to vaporize said non-naphthalenic components together with said N-methyl-forrnemide as a minimumboiling azeotropic distillate, thereby leaving as azeotropic bottoms a product in which the ratio of napfhthalenic to non-naphthalenic hydrocarbons is substantially greater than the ratio thereof in said hydrocarbon mixture.

2. A process as defined by claim 1 `wherein said azentropic distillate is condensed and allowed to stratify in the presence of an added material having the property ot reducing the normal miscibility of N-methyl-formarnide and said non-naphthalenic components.

3. A process as defined by claim 1 ywherein the naphthalenic components of said hydrocarbon |mixture include Y naphthalene and methyl-naphthalenes. 4. A process as defined by claim 1 wherein said hydro carbon mixture is one obtained `by fractionally distilling a product obtained by the catalytic idealkylation of a,

platinumcatalyzed reformate inaction boiling between about 385 F. and about 440 F.

5. A process as defined by claim 2 wherein said added materia is water.

` 6. A process for treating `a hydrocarbon mixture boiling within the range from about 390'u F. to about 520 F and comprising naphthalenic and .non-naphtnalenic componente which are not separable by simple fractional distillation, which process comprises introducing said hy-. drocarbon mixture into la distillation column together with sullicient added N-methylormamide to yiaporize said Vnon-naphtilalenic components together with said N-meth yl-tormamide as a minimum-boiling azeotropic distillate; withdrawing said distillate from said column as an overhead stream; condensing s-aid distillate and allowing the Vazeotropic condensate 'to separate 'by gravity into upper and lower liquid phases; returning the lower phase to said column; 'fractionally distilling the upper phase; condensing the distillate so obtained and allowing the condensate to sepa-rate into upper and lower phase; returning the upper phase to the said fractional distillation step; and withdrawing Ifrom said distillation column a bottoms fraction rich in naphthalenic components of said hydrocarbon mixture.

7. A process as dened by claim 6 lwherein the naphthalenic components of said hydrocarbon mixture include naphthalene and methyl-naphthalenes.

S. A process as delined by claim 7 wherein the said azeotropic condensate is separated into said upper and lower layers in the presence of an added material capable of reducing the normal miscibi'lity of N-methyl-formamide and said non-naphthalenic components.

9. A process as defined by claim 8 wherein the said ladded material is water.

References Cited in the file of this patent UNITED STATES PATENTS 

6. A PROCESS FOR TREATING A HYDROCARBON MIXTURE BOILING WITHIN THE RANGE FROM ABOUT 390* F. TO ABOUT 520* F., AND COMPRISING NAPHTHALENIC AND NON-NAPHTHALENIC COMPONENTS WHICH ARE NOT SEPARABLE BY SIMPLE FRACTIONAL DISTILLATION, WHICH PROCESS COMPRISES INTRODUCING SAID HYDROCARBON MIXTURE INTO A DISTILLATION COLUMN TOGETHER WITH SUFFICIENT ADDED N-METHYL-FORMAMIDE TO VAPORIZE SAID NON-NAPHTHALENIC COMPONENTS TOGETHER WITH SAID N-METHLY-FORMAMIDE AS A MINIMUM-BOILING AZEOTROPIC DISTILLATE; WITHDRAWING SAID DISTILLATE FROM SAID COLUMN AS AN OVERHEAD STREAM; CONDENSING SAID DISTILLATE AND ALLOWING THE AZEOTROPIC CONDENSATE TO SEPARATE BY GRAVITY INTO UPPER 